1. Field of the Invention
The present invention relates to an optical pickup apparatus used in an optical head apparatus or an optical disk apparatus for recording or reproducing data to or from an optical recording medium such as, for example, an optical disk or a magneto-optical disk.
2. Description of the Related Art
Conventionally, an optical recording medium or a disk is used for storing video and audio information or computer data. In recent years, there has been a strong demand for a higher density and larger capacity optical recording medium.
The recording density of a recording medium can be improved by, for example, increasing a numerical aperture (hereinafter, referred to as an xe2x80x9cNAxe2x80x9d) of an objective lens provided in the optical pickup apparatus or shortening the wavelength of light emitted by a laser device provided as a light source. However, increasing the NA of the objective lens requires a distance from the objective lens to the recording medium to be reduced. The objective lens having a high NA has larger aberration than an objective lens having a low NA. The aberration is caused by a tilt of the recording medium with respect to the objective lens. Under such circumstances, there has been proposed a method of reducing the thickness of a glass cover of the recording medium so as to reduce the aberration, so that recording or reproduction of data to or from such a recording medium is performed using an objective lens having a high NA and light having a shorter wavelength.
However, it is difficult to reproduce information from conventional CDs, DVDs or other types of disks using an objective lens having a high NA since the conventional disks are designed to have data stored thereon reproduced using an objective lens having a low NA. Accordingly, in order to reproduce data stored on the conventional CDs or DVDs in an optical pickup apparatus designed for a high-density, large-capacity disks, the optical pickup apparatus needs to include an objective lens having a low NA for the conventional CDs or DVDs in addition to an objective lens having a high NA.
FIG. 14 shows an optical pickup apparatus 300 disclosed in Japanese Laid-Open Publication No. 11-120587. The optical pickup apparatus 300 includes a holder 55. The holder 55 accommodates a first optical system 52 having a high NA including a first objective lens 50 and a second objective lens 51, and a second optic system having a low NA, i.e., a third objective lens 53 (the second optical system will sometimes be indicated by reference numeral xe2x80x9c53xe2x80x9d for the sake of convenience). The first optical system 52 is provided for recording or reproducing data to or from a first disk 71, and the second optical system 53 is provided for recording or reproducing data to or from a second disk 70. The optical pickup apparatus 300 uses the first optical system 52 or the second optical system 53 in accordance with which of the disk 70 or 71 is used. Since the first optical system 52 and the second optical system 53 have different NAs from each other, the first objective lens 50 and the third objective lens 53 are located so as to be away from the first disk 71 and from the second disk 70 by different distances.
The conventional optical pickup apparatus 300 having such a structure involves the following problems.
(1) The difference between the distance from the first objective lens 50 to the first disk 71 and the distance from the third objective lens 53 to the second disk 70 are adjusted to be set distances, respectively, by the position of the holder 55. Accordingly, when the second optical system having a low NA (i.e., the third objective lens 53) becomes uncontrollable in the direction of an optical axis thereof while the second disk 70 is being used for recording or reproduction (i.e., the second optical system 53 is used), the first optical system 52 may possibly collide against the second disk 70 resulting in the second disk 70 or the fist optical system 52 being damaged.
(2) In the case where the third objective lens 53 (i.e., the second optical system having a low NA) and the first objective lens 50 included in the first optical system 52 having a high NA are located on substantially the same plane, the following problems occur. The distance between the first disk 71 and the first optical system 52 which is required to record or reproduce data to or from the first disk 71 is significantly different from the distance between the second disk 70 and the second optical system 53 which is required to record or reproduce data to or from the second disk 70. Therefore, when the first optical system 52 is switched to the second optical system 53 or vice versa, the holder 55 needs to be moved a distance which is too far to guarantee an appropriate tilt of the disk with respect to the respective objective lens.
xe2x80x9c(3) In the above-described case, a DC current needs to be continuously supplied to the holder 55 in order to move the holder 55 to a prescribed position to obtain the required distance from the optical system and the objective lens. This increases the power consumption.xe2x80x9d
An optical pickup apparatus according to the present invention includes a first optical system for recording or reproducing signals to or from a first optical recording medium; a second optical system for recording or reproducing signals to or from a second optical recording medium; a holder for accommodating the first optical system and the second optical system on substantially the same plane; a focusing driving device for moving the holder in a first direction parallel to an optical axis of the first optical system and the second optical system; a tracking driving device for rotating the holder in a second direction perpendicular to the optical axis of the first optical system and the second optical system; a switching device for placing the first optical system on an optical path for recording or reproducing signals to or from the first optical recording medium, and for placing the second optical system on the optical path for recording or reproducing signals to or from the second optical recording medium, and a variable distance driving device for varying a distance between the first optical recording medium and the first optical system from a distance between the second optical recording medium and the second optical system when one of the first optical system and the second optical system is switched to the other optical system.
In one embodiment of the invention, the variable distance driving device drives the holder in a direction of the optical axis.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by a magnetic repulsive force.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by the magnetic repulsive force when the holder is not moving in the second direction or when one of the first optical system and the second optical system is switched to the other optical system.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by a magnetic attractive force.
In one embodiment of the invention, the variable distance driving device drives the holder in the direction of the optical axis by the magnetic attractive force when the holder is not moving in the second direction or when one of the first optical system and the second optical system is switched to the other optical system.
In one embodiment of the invention, the variable distance driving device moves the holder when the first optical recording medium or the second optical recording medium is mounted on the optical disk apparatus such that a distance from the recording medium to the holder is larger than a prescribed distance from the second recording medium to the holder when the second optical system is located in the optical path.
Thus, the invention described herein makes possible the advantages of providing an optical pickup apparatus which prevents collision between a disk and an objective lens when the required distance between the disk and the objective lens is different depending on the disk to be used, and thus is usable for recording or reproducing data to or from optical recording media of a plurality of different specifications.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.